The highly successful erotic novel was released in 2011, and fans have been speculating about who might portray the two main characters since plans for a film were announced last year. A psychology lecturer at the University of Central Lancashire even put a face to the character of billionaire Grey, who has had readers all aflame.

Now, the fantasy will come to life in the form of Hunnam, who is one of the stars of the film "Pacific Rim" and the television series "Sons of Anarchy."

Johnson is the daughter of actors Melanie Griffith and Don Johnson and has appeared in the films "The Five-Year Engagement" and "21 Jump Street."